1. Field of the Invention
The present invention relates to a novel poly(1,3-propylene terephthalate), and more particularly relates to a novel process for preparing the poly(1,3-propylene terephthalate) by reacting terephthalic acid and 1,3-propanediol in the presence of ethylene glycol titanate as an esterification catalyst and antimony acetate as a polymerization catalyst.
2. Description of the Prior Art
Early in 1941, poly(1,3-propylene terephthalate) (PPT) has been synthesized by Whinfield and Dickson, and it is known that the physical properties of PPT is superior than those of poly(ethylene terephthalate) (PET). At that time, ethylene glycol, which is the starting material of PET, can be commercially prepared, while 1,3-propandiol, which is the starting material of PPT, still can not be commercially prepared. Therefore, PET has first been mass-produced in industry, while PPT has been not. Also, the progress in the techniques for synthesize PPT is limited, and the obtained PPT has an inadequate molecular weight and unacceptable physical properties.
Recently, novel processes for synthesize PPT have been disclosed in Japanese Kokai 51-140298 and U.S. Pat. No. 5,340,909, which focus on improving thermal stability and yellowness, and increasing intrinsic viscosity (IV). However, one is because the monomer used is limited to dimethylene terephthalate (DMT), and the other is because the lowest yellowness b* of the product can only be 9 to 7.5, which reaches below 4 only by the incorporation of pigments; therefore, the results are not satisfactory.
Recently, the techniques for determining structures and physical properties of polymers have progressed greatly, such that we can know the structures and physical properties of PPT for a further extent. Theoretically, since PPT has a larger crystalline structure unit and gauche-gauche molecular conformation than PET, therefore PPT has better bending recovery and the dye molecular will have greater chance to deposit on the PPT crystal. Practically, indeed, experimental results show that the PPT fiber has close bending recovery to nylon 66, and PPT can be dyed at atmospheric pressure without using any dyeing carrier agent. Therefore, if the techniques for synthesizing PPT can be improved and the problems in the conventional process for preparing PPT can be solved, PPT will become a potential commercial polymer for the new century.